Magnetic field detector system

ABSTRACT

Aspects and embodiments are generally directed to magnetic field detector systems and methods. In one example, a magnetic field detector system includes a proof-mass including a magnetic dipole source, a plurality of supports, each individual support of the plurality supports being coupled to the proof-mass, a plurality of sensors, each individual sensor of the plurality of sensors positioned to measure a resonant frequency of a corresponding support of the plurality of supports, and a controller coupled to each individual sensor of the plurality of sensors, the controller configured to measure a characteristic of a magnetic field imparted on the proof-mass based on at least a first resonant frequency of the measured resonant frequencies.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 62/237,841, titled “ELECTRIC FIELD DETECTOR SYSTEM,” filed on Oct. 6, 2015, which is hereby incorporated herein by reference in its entirety. This application also claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 62/370,367, titled “MAGNETIC FIELD DETECTOR SYSTEM,” filed on Aug. 3, 2016, which is hereby incorporated herein by reference in its entirety.

BACKGROUND

Equipment that is electrically operated, or that incorporates moving structures containing electrically conductive materials or charged dielectrics, will generate static and time-varying electromagnetic fields during operation. These fields may be faint even in close proximity to the source, and will attenuate as the distance from the source is increased. Nevertheless, detectable components of these signals may exist at great distances from the source. Often great care is taken to design equipment, such as military equipment, to minimize the likelihood that unintended electromagnetic emissions will reveal the location of the equipment. Despite the care taken to reduce such emissions, low level electromagnetic signals may still exist at great distances and can be measured. Weak electromagnetic signals may also be utilized in numerous other applications, such as in communication systems, natural resource exploration, scientific research, meteorological monitoring, localization, and navigation.

SUMMARY

Aspects and embodiments are directed to systems and methods for exploiting the magnetic component of electromagnetic signals. There is a need for improved detectors which enhance the ability to measure small fields emitted by equipment or natural processes while operating in the large background magnetic field of the Earth. Examples of the systems discussed herein may include one or more magnetic field detectors capable of detecting a magnetic field generated by equipment that has been designed to reduce unintended electromagnetic emissions, or that naturally generates very small or attenuated electric and magnetic field signals. In further aspects and embodiments, one or more of the magnetic field detectors described herein permits the detection and analysis of weak communication or navigation signals which are generated from a distant electromagnetic source.

The performance of a magnetic field detector is generally limited by the noise that contributes to its measurement. Operation of the detector and environmental conditions both contribute to the noise, which affects the resolution of the system. Conventional detectors experience difficulty measuring weak magnetic field signals in the presence of the large background magnetic field of the Earth. Accordingly, there is a need for an improved magnetic field detector capable of observing weak magnetic fields over a large dynamic range.

According to certain aspects, an improved magnetic field detector system is provided. In one example, the system includes a proof-mass including a magnetic dipole source, a plurality of supports, each individual support of the plurality supports being coupled to the proof-mass, a plurality of sensors, each individual sensor of the plurality of sensors positioned to measure a resonant frequency of a corresponding support of the plurality of supports, and a controller coupled to each individual sensor of the plurality of sensors, the controller configured to measure a characteristic of a magnetic field imparted on the proof-mass based on at least a first resonant frequency of the measured resonant frequencies.

According to certain embodiments, the controller is further configured to determine a linear force imparted on the proof-mass, in a first direction, based on at least the first resonant frequency of the measured resonant frequencies. In one example, the controller is further configured to determine a temperature based on a common mode signal generated from a comparison of each of the measured resonant frequencies. In some examples, the characteristic of a magnetic field includes a magnetic field strength, and in measuring the characteristic of the magnetic field the controller is configured to compare at least the first resonant frequency to a first frequency reference to measure a torque on the proof-mass. According to some examples, the measured resonant frequency of each individual support includes a natural frequency.

According to one embodiment, the plurality of supports includes a first support coupled to a first side of the proof-mass and having the first resonant frequency, a second support coupled to a second side of the proof-mass and having a second resonant frequency, a third support coupled to the first side of the proof-mass and having a third resonant frequency, and a fourth support coupled to the second side of the proof-mass and having a fourth resonant frequency. In one example, the controller is further configured to determine a first linear force imparted on the proof-mass in a first direction and a second linear force imparted on the proof-mass in a second direction based on the first resonant frequency, the second resonant frequency, the third resonant frequency, and the fourth resonant frequency, and determine a temperature based on a common mode signal generated from a comparison of each of the first resonant frequency, the second resonant frequency, the third resonant frequency, and the fourth resonant frequency.

In one embodiment, the magnetic dipole source is a permanent magnetic material. The permanent magnetic material may be at least one of a Neodymium Iron Boron (NdFeB) magnet, a Samarium Cobalt (SmCo) magnet, and an Alnico (AlNiCo) magnet. In certain examples, the magnetic dipole source includes a plurality of permanent magnetic materials magnetized in a common direction. In an embodiment, the magnetic dipole source is a time-varying magnetic material. In a further embodiment, the time-varying magnetic material is a soft magnetic material configured to receive an excitation signal of a predetermined frequency. In a further embodiment, the soft magnetic material is Magnesium Zinc Ferrite.

In an embodiment, each sensor of the plurality of sensors includes a comb drive including a first electrode configured to apply a voltage to a comb positioned on the corresponding support, and a second electrode configured to measure a change in a capacitance between the first electrode and the second electrode, and the controller is further configured to infer the resonant frequency of the corresponding support based at least in part on the change in the capacitance.

According to one embodiment, the system further includes a field concentrator located adjacent a side of the proof-mass, the field concentrator positioned so as to focus the magnetic field on the proof-mass. In one example, the system further includes a housing, and the system is disposed within the housing. In a further example, the housing includes a magnetic shield positioned to isolate the system from interference noise.

As discussed above, according to certain embodiments, the system further includes a housing, the system being disposed within the housing. In one example the housing includes at least one attachment to secure the system to a mobile platform. According to another example the housing includes at least one attachment to secure the system to a stationary platform.

In one embodiment, the system further includes a plurality geometric isolation structures interposed between the proof-mass and each of the plurality of supports, each geometric isolation structure being positioned to isolate a respective support from a differential thermal strain between the proof-mass and the respective support. In one example, the system further includes an internal isolation structure extending through the proof-mass and configured to suspend the proof-mass relative to a system substrate, the internal isolation structure being positioned to isolate the plurality of supports from a differential thermal strain between the proof-mass and the plurality of supports.

Certain aspects are directed to a magnetic field transduction method. In one example, the transduction method includes generating a magnetic dipole at a proof-mass coupled to a plurality of supports, receiving a magnetic field at the proof-mass, measuring a resonant frequency of each individual support of the plurality of supports, and determining a characteristic of the magnetic field based on at least one resonant frequency of the measured resonant frequencies of the individual supports.

According to one embodiment, determining the characteristic of the magnetic field further includes comparing the at least one resonant frequency to a frequency reference and determining a torque imparted on the proof-mass. In one embodiment, determining the characteristic of the magnetic field includes determining the strength and variability of the magnetic field. According to certain embodiments, the method further includes determining a linear force imparted on the proof-mass in a first direction based on the at least one resonant frequency of the measured resonant frequencies of the individual supports. The method may further include determining a temperature based on a common mode signal generated from a comparison of each of the measured resonant frequencies of the plurality of supports. The method may further include determining a force of acceleration imparted on the proof-mass based on the at least one resonant frequency of the measured resonant frequencies of the individual supports.

In one embodiment, the measured resonant frequency of each individual support of the plurality of supports includes a natural frequency. In one example, the method further includes optically sensing a displacement of the proof-mass responsive to receiving the magnetic field. According to some examples, the method further includes sensing a variation in a capacitance between the proof-mass and a reference structure responsive to receiving the magnetic field.

According to one embodiment, the plurality of supports includes a first support having a first resonant frequency, a second support having a second resonant frequency, a third support having a third resonant frequency, and a fourth support having a fourth resonant frequency, and the method further includes determining a first linear force imparted on the proof-mass in a first direction based on the first resonant frequency, the second resonant frequency, the third resonant frequency, and the fourth resonant frequency, determining a second linear force imparted on the proof-mass in a second direction based on the first resonant frequency, the second resonant frequency, the third resonant frequency, and the fourth resonant frequency, and determining a temperature based on a common mode signal generated from a comparison of each of the first resonant frequency, the second resonant frequency, the third resonant frequency, and the fourth resonant frequency.

According to certain aspects, provided is a transduction method. In one example, the method includes generating a magnetic dipole at a proof-mass coupled to a plurality of supports, receiving a bio-physical signal at the proof-mass, measuring a resonant frequency of each individual support of the plurality of supports, and determining a characteristic of the bio-physical signal based on at least one resonant frequency of the measured resonant frequencies of the individual supports.

In one embodiment, the bio-physical signal includes a magnetic field of a body of a patient. According to certain examples, the magnetic field of the body of the patient includes a magnetic field of a brain, heart, nerve, or muscle, of the patient.

According to certain aspects, provided is a transduction method. In one example, the method includes generating a magnetic dipole on a structure, and imparting a torque on the structure responsive to receiving a field.

According to one embodiment, the structure includes a proof-mass coupled to a plurality of supports, and the method further includes measuring a resonant frequency of at least one support of the plurality of supports to determine the torque imparted on the proof-mass. According to one embodiment, the field includes a magnetic field, and the method further comprises determining a strength of the magnetic field. In one embodiment, the method further includes determining an ambient temperature based on a common mode signal generated from a comparison of resonant frequencies of each individual support of the plurality of supports.

In one embodiment, the method further includes determining a linear force imparted on the proof-mass in a first direction based on at least one resonant frequency of at least one of the plurality of supports. According to one embodiment, the method further includes isolating the plurality of supports from a differential thermal strain between the proof-mass and the plurality of supports. In an embodiment, the method further includes measuring the displacement of the structure by measuring the change in capacitance between the structure and a reference structure. In an embodiment, the method further includes measuring displacement of the structure to infer the torque imparted on the proof-mass.

According to an aspect, provided is a transduction method. In one example, the transduction method includes generating a magnetic dipole at a proof-mass coupled to a plurality of supports, receiving a magnetic field at the proof-mass, optically sensing a displacement of the proof-mass responsive to receiving the magnetic field, and determining a characteristic of the magnetic field based on at least on the displacement of the proof-mass.

According to another aspect, provided is another transduction method. In one example, the transduction method includes generating a magnetic dipole at a proof-mass coupled to a plurality of supports, receiving a magnetic field at the proof-mass, sensing a variation in a capacitance between the proof-mass and a reference structure responsive to receiving the magnetic field, and determining a characteristic of the magnetic field based on at least the variation in the capacitance between the proof-mass and the reference structure.

Still other aspects, embodiments, and advantages of these exemplary aspects and embodiments, are discussed in detail below. Moreover, it is to be understood that both the foregoing information and the following detailed description are merely illustrative examples of various aspects and embodiments, and are intended to provide an overview or framework for understanding the nature and character of the claimed aspects and embodiments. Any embodiment disclosed herein may be combined with any other embodiment in any manner consistent with at least one of the objectives, aims, and needs disclosed herein, and references to “an embodiment,” “some embodiments,” “an alternate embodiment,” “various embodiments,” “one embodiment” or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment. The appearances of such terms herein are not necessarily all referring to the same embodiment. Various aspects, embodiments, and implementations discussed herein may also include means for performing any of the recited features or functions.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of the invention. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures:

FIG. 1 is a block diagram of one example of a magnetic field detector system according to aspects of the present disclosure;

FIG. 2 is a side view of the block diagram of the magnetic field detector system illustrated in FIG. 1, according to aspects of the present disclosure;

FIG. 3 is a graph demonstrating the relationship between resonant frequency and support tension according to aspects of the present disclosure;

FIG. 4 is a graph demonstrating the improved noise sensitivity of a magnetic field detector system according to aspects of the present disclosure;

FIG. 5 is a block diagram of one example of a controller according to aspects of the present disclosure;

FIG. 6 is a perspective view of an example of an arrangement of a magnetic field detector according to aspects of the present disclosure;

FIG. 7 is another perspective view of an example of an arrangement of a magnetic field detector according to aspects of the present disclosure;

FIG. 8 is a perspective view of one example of a magnetic field detector system including geometric isolation structures, according to aspects of the present disclosure;

FIG. 9A is a perspective view of one example of a magnetic field detector system including geometric isolation structures, according to aspects of the present disclosure;

FIG. 9B is a plan view of the magnetic field detector system illustrated in FIG. 9A, according to aspects of the present disclosure; and

FIG. 10 is a diagram of an example of a magnetic field detector system packaged within a housing, according to aspects of the present disclosure.

DETAILED DESCRIPTION

Aspects and embodiments are generally directed to magnetic field detector systems and methods for exploiting the magnetic component of electromagnetic signals. Systems may include one or more magnetic field detectors capable of detecting a magnetic field generated by equipment or natural processes that generate electromagnetic fields. Systems may also include one or more magnetic field detectors capable of detecting bio-physical signals generated by the body of a patient or user, such as the magnetic fields his or her brain, heart, nerves or muscles.

Current magnetic field detectors include high noise sensors that inhibit the observation of weak electric field signals at low frequencies or low noise sensors which are difficult to practically implement. For example, superconducting quantum interference devices (SQUID) require operation at cryogenic temperatures. While various atomic sensors can provide low noise performance, they are challenging to operate with low noise performance as a result of the Earth's large background magnetic field. Similarly, inductive search coils experience high noise at low frequencies. Moreover, each of these solutions is large in size and physically restrictive, which is not practical in most military or mobile applications. Accordingly, certain aspects and embodiments provide improved magnetic field detection systems and methods, as discussed below.

In certain examples, systems described herein are enabled by the use of one or more magnetic dipole sources (e.g., magnetic material) coupled to a proof-mass which can be measured to infer characteristics of a magnetic field. The magnetic dipole source generates a magnetic dipole, which produces a torque when exposed to a magnetic field. The torque imparted on the proof-mass can be determined (e.g., directly or indirectly measured) to infer the magnetic field characteristic, for example, a magnetic field strength. In one embodiment, the proof-mass is coupled to one or more mechanical supports each having a resonant frequency which can be measured to determine the torque and strength of the magnetic field. In various embodiments, the system further measures acceleration (e.g., linear acceleration or rotational acceleration) and temperature in addition to, or simultaneously with, the strength of the magnetic field.

It is to be appreciated that examples and/or embodiments of the methods and systems discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The methods and systems are capable of implementation in other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, acts, elements and features discussed in connection with any one or more examples and embodiments are not intended to be excluded from a similar role in any other example or embodiment. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use herein of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms. Any references to front and back, left and right, top and bottom, upper and lower, and vertical and horizontal are intended for convenience of description, not to limit the present systems and methods or their components to any one positional or spatial orientation.

The accompanying drawings are included to provide illustration and a further understanding of the various aspects and examples, and are incorporated in and constitute a part of this specification. The drawings, together with the remainder of the specification, serve to explain principles and operations of the described and claimed aspects and examples.

FIG. 1 illustrates a block diagram of one example of a magnetic field detector system 100 according to various aspects and embodiments. The system 100 is shown as including a proof-mass 102 including a magnetic dipole source, a plurality of supports (e.g., first support 104, second support 106, third support 132, and fourth support 138), a plurality of sensors each including a first electrode and a second electrode (i.e., a first sensor including first electrode 108 and second electrode 109, a second sensor including first electrode 110 and second electrode 111, a third sensor including first electrode 134 and second electrode 135, and a fourth sensor including first electrode 140 and second electrode 141) a controller 112, a displacement sensor 114, field concentrators 116, and a housing 118. While shown as including four supports, in further embodiments the system 100 may include any number of supports and electrode configurations. In particular, while each of the first support 104, second support 106, third support 132, and fourth support 138 are illustrated as a single beam in FIG. 1, in various other embodiments each support 104, 106, 132, 138 may be split into a double-beam fork to further reduce damping losses. In FIG. 1, the proof-mass 102 is shown as being formed from a magnetic material; however, in other implementations the proof-mass 102 may be coupled (e.g., adhered or connected) to the magnetic dipole source.

As shown, in one embodiment the first support 104 is coupled between a first side 120 of the proof-mass 102 and a first mechanical ground 124. The first support 104 may include a first comb interposed between the proof-mass 102 and the mechanical ground 124. In such an embodiment, the first comb of the first support 104 may be positioned between, and in electrical communication with, the first electrode 108 and second electrode 109 of the first sensor. Similarly, the second support 106 is coupled between a second side 122 of the proof-mass 102 and a second mechanical ground 126. The second support 106 may include a second comb interposed between the proof-mass 102 and the second mechanical ground 126. In such an embodiment, the second comb of the second support 106 may be positioned between, and in electrical communication with, the first electrode 110 and the second electrode 111 of the second sensor. The third support 132 is coupled between the first side 120 of the proof-mass 102 and a third mechanical ground 136. The third support 132 may include a third comb interposed between the proof-mass 102 and the third mechanical ground 136. In such an embodiment, the third comb of the third support 132 may be positioned between, and in electrical communication with, the first electrode 134 and second electrode 135 of the third sensor. Similarly, the fourth support 138 is coupled between the second side 122 of the proof-mass 102 and a fourth mechanical ground 142. The fourth support 138 may include a fourth comb interposed between the proof-mass 102 and the fourth mechanical ground 142. In such an embodiment, the fourth comb of the fourth support 138 may be positioned between, and in electrical communication with, the first electrode 140 and the second electrode 141 of the fourth sensor. The second side 122 of the proof-mass 102 is shown substantially opposite to the first side 120 of the proof-mass 102. Each mechanical ground may be further coupled to, or formed on, a shared substrate.

In various examples, the first support 104, second support 106, third support 132, and fourth support 138 act like springs. Movement of the proof-mass 102 is constrained by the spring force of each support, damping forces, and inertial forces. FIG. 1 shows the first support 104, second support 106, third support 132, and fourth support 138, coupled to the proof-mass 102 at an angle substantially perpendicular to the respective surfaces of the proof-mass 102. In certain embodiments, any or all of the first support 104, the second support 102, the third support 132, and the fourth support 138, may be coupled to surfaces of the proof-mass at predetermined angles. Such a configuration may permit detection of axial forces in two linear directions. The ghost-line 144 shown in FIG. 1 demonstrates an illustrative angle α at which the first support 104 may be attached. The second, third, and fourth support 106, 132, 138 may be attached in a similar manner. As the proof-mass 102 may have a plurality of surfaces, in varying embodiments, supports may be attached to any suitable surface of the proof-mass 102. FIG. 2 illustrates an example of a side view of the system 100 according to various embodiments. Views of the second support 106, second sensor, fourth support 138, and fourth sensor are obscured by the first support 104, the first sensor, the third support 132, and the third sensor.

As shown in FIG. 2, the proof-mass 102 may be defined by a length (not shown in FIG. 2), width (w), and height (h). For example, in one implementation the length may be 2000 μm, the width (w) may be 500 μm, and the height (h) may be 500 μm. Similarly, the one or more field concentrators 116 may be positioned at a predetermined distance d₁ from the proof-mass 102, and defined by a length (not shown), width (x), and height (y). In one implementation, the one or more concentrators 116 may have dimensions of 50 mm by 2 mm by 0.4 mm, and a gain of 75. In such an arrangement, the concentrators 116 may be arranged at a distance of 200 μm from the proof-mass 102. It is appreciated that variations in the dimensions of the proof-mass 102 may affect the characteristics of the magnetic dipole. For example, increasing the size of the proof-mass 102 (and resulting increase in the dimensions of the magnetic dipole source) may result in an increase in the sensitivity to an imparted magnetic field.

Returning to FIG. 1, the magnetic dipole source generates a magnetic dipole which produces a torque on the proof-mass 102 when exposed to a magnetic field. The torque imparted on the proof-mass 102 generates an axial force on the plurality of supports (i.e., first support 104, the second support 106, the third support 132, and the fourth support 138). The torque may be determined directly, or indirectly, to determine one or more characteristic of the magnetic field, such as the magnetic field strength. For example, such axial forces will modify a resonant frequency (e.g., natural frequency) of each support. This may include a first resonant frequency of the first support 104, a second resonant frequency of the second support 106, a third resonant frequency of the third support 132, and a fourth resonant frequency of the fourth support 138. Each support resonates at a particular mechanical resonance when no force is applied. In various embodiments, the controller 112 is coupled to the first electrode 108 and the second electrode 109 of the first sensor, the first electrode 110 and the second electrode 111 of the second sensor, the first electrode 134 and the second electrode 135 of the third sensor, and the first electrode 140 and the second electrode 141 of the fourth sensor. Each sensor is positioned to measure the resonant frequency of the adjacent support and provide a corresponding signal to the controller 112.

For example, the first sensor measures the first resonant frequency of the first support 104, the second sensor measures the second resonant frequency of the second support 106, the third sensor measures the third resonant frequency of the third support 132, and the fourth sensor measures the fourth resonant frequency of the fourth support 138. The controller 112 is coupled to and in communication with each sensor and configured to execute a series of operations to determine the magnetic field strength of the magnetic field imparted on the proof-mass 102 based on the measured resonant frequency of at least one support.

In various embodiments, the plurality of sensors (i.e., the first sensor, second sensor, third sensors, and fourth sensor) may each include a comb drive including a motor component and a sense component positioned on either side of the illustrated comb of a support. However, in various other embodiments, the sensors may include any other capacitive actuator. For example, the first electrode (e.g., electrodes 108, 110, 134, 140) of each sensor may include the motor component and the second electrode (e.g., electrodes 109, 111, 135, 141) may include the sense component. Alternatively, the second electrode of each sensor may include the motor component and the first electrode may include the sense component.

Each of the motor component and sense component are coupled to and in communication with the controller 112, as shown in FIG. 1. A voltage applied by the motor component causes the motor component, comb, and sense component to be drawn together. The resonant frequency of each support (e.g., first support 104, second support 106, third support 132, and fourth support 138) is proportional to the force developed by the respective sensor. A comb drive capacitance of each sensor may be used to measure the resonant frequency of the support. In particular examples, the controller 112 manages a gain and phase between the motor component and the sense component of each sensor to realize an oscillator which resonates the respective support. In certain other examples, the controller may also manage each sensor to rebalance the system 100 and null changes in the resonator natural frequency.

The axial force exerted on each support as a result of the torque on the proof-mass 102 will cause the support to expand or compress. Stretching will increase the resonant frequency and compression will decrease in the resonant frequency. In several embodiments, the controller 112 receives measured signals from the plurality of sensors, and the resonant frequency is measured according to:

$f = {f_{o}\sqrt{1 + {\frac{L^{2}}{\pi^{2}{EI}}P}}}$

where, f_(o) corresponds to the initial resonant frequency at a predetermined value, L corresponds to the dimensions of the proof-mass, E corresponds to the applied voltage, I corresponds to the dimensions of the support, and P corresponds to the strength of the magnetic field generated by the magnetic dipole source. In various embodiments, the controller 112 operates in concert with the motor component and sense component of each sensor as an oscillator loop with the resonant frequency as the output.

Various embodiments of the sensors discussed herein may further include a force multiplier positioned to increase the force experienced by each sensor. While in one embodiment, changes in frequency may be used to detect the strength of a magnetic field, in other embodiments they may be used to detect an acceleration or a change in temperature. As shown in FIG. 1, in one embodiment, the supports may be arranged such that when one support is compressed (e.g., first support 104 is compressed), a second support is expanded (e.g., second support 106 is expanded), or vice versa.

In various embodiments, the controller 112 compares at least one measured resonant frequency, such as the first resonant frequency, to a resonant frequency reference. The frequency reference may include the initial resonant frequency of the particular support, as mentioned above. Based on the comparison, the controller 112 determines the change in resonant frequency to ascertain the torque on the proof-mass 102. The torque on the proof-mass 102 induces the axial force at the end of the respective supports, as also discussed above. Accordingly, the resonant frequency changes as a function of the force during operation of the system 100.

FIG. 3 shows a plot of the relationship between the resonant frequency and the tension in a support, according to various embodiments. As indicated by trace 302, the resonant frequency increases as the tension increases, and decreases as the tension decreases. Accordingly, the torque determined from the resonant frequency, and in particular the change in resonant frequency, may be used by the controller 112 to determine the strength of the magnetic field. In various embodiments, the resonant frequency includes the natural frequency of the respective support. In one example, the controller 112 may execute a series of instructions to determine the magnetic field strength according to:

T=m×B

where, m is the strength (A−m²) of the magnetic dipole on or attached to the proof-mass, τ is the torque (N−m) on the proof-mass, and B is the magnetic field strength (T).

Similarly, the controller 112 may determine the force of acceleration on the proof-mass 102 based on at least one resonant frequency of the plurality of supports. As described above, with no stress or force on the plurality of supports (i.e., first support 104, second support 106, third support 132, and fourth support 138), the resonant frequency of each support will be a predetermined value (e.g., a resonant frequency reference). An axial force imparted on each support will either push or pull the support, thereby increasing or decreasing the resonant frequency of the respective support. The difference between the resonant frequency and the resonant frequency reference represents the force of the acceleration. While in one example, the determined acceleration may include a linear acceleration, in certain other examples the determined acceleration may include a rotational direction.

In further embodiments, a variance in ambient temperature can cause an expansion or compression of the plurality of support members (e.g., support 104, 106, 132, and 138). Such a variance acts like an axial force imparted on the plurality of supports and causes an increase or decrease in the resonant frequency of each respective support. While in some instances, embodiments may include supports that are largely insensitive to temperature changes, in other embodiments, the resonant frequency from one or more supports may be compared to generate a common mode signal. As used herein, a common mode signal may include a component of an analog signal that is common to the plurality of supports (e.g., the support 104, the second support 106, the third support 132, and the fourth support 138). It is appreciated that ambient temperature changes will have equal effects on each of the plurality of supports. Therefore, various embodiments of the controller 112 discussed herein may be configured to determine a temperature, or one or more temperature changes, based on the common mode signal.

Accordingly, in one embodiment, such as that shown in FIGS. 1 and 2, the resonant frequencies of four supports may be measured to determine a torque on the proof-mass, a first linear force in a first direction, a second linear force in a second linear direction, and a temperature. It is appreciated that additional supports may be added to determine additional degrees of freedom. In one example, the torque (τ), first linear force (a_(x)), second linear force (a_(y)), and temperature (T), may be determined based on calibration coefficients and the measured resonant frequencies of the plurality of supports (f_(A), f_(B), f_(C), and f_(D)) according to:

${\begin{bmatrix} {ka}_{\tau} & {kb}_{\tau} & {kc}_{\tau} & {kd}_{\tau} \\ {ka}_{ax} & {kb}_{ax} & {kc}_{ax} & {kd}_{ax} \\ {ka}_{ay} & {kb}_{ay} & {kc}_{ay} & {kd}_{ay} \\ {ka}_{T} & {kb}_{T} & {kc}_{T} & {kd}_{T} \end{bmatrix} \cdot \begin{bmatrix} f_{A} \\ f_{B} \\ f_{C} \\ f_{D} \end{bmatrix}} = {\begin{bmatrix} \tau \\ a_{x} \\ a_{y} \\ T \end{bmatrix}.}$

Higher order equations and compensation routines may leverage external stimuli such as auxiliary sensors (e.g., gyroscopes, accelerometers, and thermistors) to improve the fidelity of the determinations. The auxiliary sensors may reduce the contribution from error sources and can be used to isolate the received magnetic signal from interference effects and error sources.

FIG. 1 shows the proof-mass 102 as having a substantially rectangular profile and having a plurality of planar surfaces. While this may be advantageous for some applications, in other applications the proof-mass 102 may be defined by non-planar surfaces and may have any suitable shape. According to various embodiments, the proof-mass 102 and the plurality of supports (e.g., supports 104, 106, 132, and 138), are made of silicon material; however, in other embodiments the proof-mass 102 and the plurality of supports may be made of any appropriate material including multiple materials coupled together. Each mechanical ground 124, 126, 136, and 142, may be further coupled, or formed on, a shared substrate, such as a glass (i.e., silicon dioxide) substrate. However, in other embodiments, the mechanical grounds may be attached to any other appropriate material (e.g., silicon). FIG. 2 shows the first mechanical ground 124 and the third mechanical ground 136 coupled to a shared substrate 210. While FIG. 2 illustrates one arrangement of the first mechanical ground 124 and the third mechanical ground 136, in certain other examples, each of the first mechanical ground 124 and the third mechanical ground 136 may have a height which is substantially the same as a distance between the proof-mass 102 and the shared substrate 210 and a height of the respective support (e.g., first support 104 or third support 132), when combined.

In various embodiments, the source of the magnetic dipole includes one or more magnetic material(s). For example, the magnetic material(s) may include one or more permanent magnetic materials such as rare Earth magnets, ferrite magnets (e.g., Neodymium Iron Boron, Samarium Cobalt, or Alnico), or other hard magnetic materials. Alternatively, the magnetic dipole source may be formed from a time-varying magnetic material, such as one or more soft magnetic material(s) (e.g., Magnesium Zinc Ferrite) excited by an external source via an excitation signal of a predefined frequency. Further embodiments may include a series of two or more stacked magnets or a plurality of magnets arranged in a predetermined order. In order to increase the strength of the magnetic dipole, and increase the sensitivity of the system to magnetic fields, multiple discrete magnets may be coupled to the proof-mass.

Various embodiments discussed herein may include one or more field concentrators located adjacent the proof-mass 102. For example, FIG. 1 shows the field concentrators 116 located proximate a third side 128 and fourth side 130 of the proof-mass 102. Field concentrators 116 may include various flux concentrators, such as soft magnetic material positioned and arranged to focus the magnetic field on the proof-mass 102. In some embodiments, field concentrators 116 are formed from soft ferrite or other material with a long and slender profile having a flare at an end. However, in further embodiments field concentrators 116 may include any appropriate structure, material, and shape.

As shown in FIG. 1, the system 100 may include a housing 118. Various components of the system 100 are located within the housing, which protects the components during handling and operation. In one particular embodiment, the housing 118 may include a cryogenic dewar. The cryogenic dewar serves as a cold shield, within which the system components may be cooled, for example, to cryogenic temperatures. Operating the system 100 at cryogenic temperatures reduces Brownian motion and further enhances the signal to noise ratio.

While described above as detecting magnetic field characteristics through the resonance frequency of one or more supports, other embodiments of the system shown in FIG. 1 may include one or more displacement sensors configured to directly measure displacement of the proof-mass. As shown in FIG. 1, one or more sensors 114 may be electrically or optically coupled to the proof-mass 102. For example, an optical sensor may direct optical radiation to and detect reflected radiation from the surface of the proof-mass 102. Movement of the proof-mass 102 may vary reflections of the radiation and enable the optical sensor to track the movement of the proof-mass 102. Although described in one implementation as including an optical sensor, in various embodiments the displacement sensor 114 may include any laser sensor capable of detecting movement of the proof-mass 102.

In other embodiments, movement of the proof-mass 102 may be determined capacitively or using any other method that indirectly determines position and/or forces imparted on the proof-mass 102. For example, the controller 112 may be configured to receive a signal from one or more reference structures, positioned proximate a surface of the proof-mass 102 (e.g., one or more capacitive sensors positioned proximate one or more of the sides 120, 122, 128, 130 and/or a top or bottom surface of the proof-mass 102), indicating a variation in a capacitance between the proof-mass 102 and the one or more reference structures. The controller 112 may then determine the discussed magnetic field characteristic(s) based on the received signal. While discussed with reference to FIG. 1 as including each of a displacement sensor 114, a capacitive reference structure, and a plurality of sensors positioned to measure a resonant frequency of a corresponding support, in several embodiments the system 100 may include the displacement sensor 114, and/or the reference structure, as an alternative to the plurality of sensors.

Accordingly, aspects and embodiments discussed above are generally directed to a system 100 for exploiting the magnetic component of electromagnetic signals. As discussed, the system 100 may include one or more magnetic field detectors capable of detecting a magnetic field generated by equipment that has been designed to reduce unintended electromagnetic emissions, equipment that naturally generates very small or attenuated electric and magnetic field signals, or beacons designed for long range communication or navigation purposes.

FIG. 4 provides a graph demonstrating the improved noise insensitivity of various embodiments when compared with known magnetic field detectors. In particular, FIG. 4 demonstrates a comparison of the noise at 1 Hz. In FIG. 4, the vertical axis 402 represents the system resolution (T/√Hz) and the horizontal axis 404 represents volume (cc). As discussed above, magnetic field detectors are typically limited by the total noise that contributes to the measurement of the magnetic field. The detector, and the natural and human environment (e.g., Earth's background magnetic field), all contribute to this total noise. Accordingly, total noise determines the system resolution (T/√Hz).

In contrast to conventional detectors, various embodiments provide an ultra-low noise detector which can observe weak magnetic field signals of interest. The same result is challenging to achieve with high noise detectors, because the signal of interest is often indistinguishable from noise in the system. As demonstrated in FIG. 4, not only do various embodiments exhibit improved sensitivity (e.g., magnetic field detector system with a field concentrator data point 406), for equivalent levels of sensitivity, embodiments are volumetrically much smaller (e.g., magnetic field detector system data point 408). Comparatively, examples of noise sensitivity of various known detectors are represented by data groups 410, 412, 414, 416, 418.

Though the components of several views of the drawings herein may be shown and described as discrete elements in a block diagram unless otherwise indicated, the electronic components (e.g., the controller 112) may be implemented as one of, or a combination of, analog circuitry, digital circuitry, or one or more microprocessors executing software instructions. For example, the software instructions may include digital signal processing (DSP) instructions. Unless otherwise indicated, signal lines may be implemented as discrete analog or digital signal lines, as a single discrete digital signal line with appropriate signal processing, or as elements of a wireless communication system. Some of the processing operations may be performed by other analog or digital signal processing techniques and are included within the scope of this application. Unless otherwise indicated, control signals may be encoded in either digital or analog form. Conventional digital-to-analog or analog-to-digital converters may not be shown in the figures.

Referring to FIG. 5, there is illustrated a block diagram of an example of a controller, in which various aspects and functions are practiced. As shown, the controller can include one or more systems components that exchange information. More specifically, the controller 500 can include at least one processor 502, a power source 514, a data storage 510, a user interface 508, a system interface 512, a memory 504, and one or more interconnection mechanisms 506. The at least one processor 502 may be any type of processor or multiprocessor. The at least one processor 502 is connected to the other system components, including one or more memory devices 504 by the interconnection mechanism 506. In various embodiments, the controller 500 can further include any appropriate signal processing circuitry, such as circuitry configured to execute signal conditioning and electronic control and feedback.

The memory 504 stores programs (e.g., sequences of instructions coded to be executable by the processor 502) and data during operation of the controller 500. Thus, the memory 504 may be a relatively high performance, volatile, random access memory such as a dynamic random access memory (“DRAM”) or static memory (“SRAM”). However, the memory 504 may include any device for storing data, such as a disk drive or other nonvolatile storage device. Various examples may organize the memory 504 into particularized and, in some cases, unique structures to perform the functions disclosed herein. These data structures may be sized and organized to store values for particular data and types of data.

Components of the controller 500 are coupled by an interconnection mechanism such as the interconnection mechanism 506. The interconnection mechanism 506 may include any communication coupling between system components such as one or more physical busses in conformance with specialized or standard computing bus technologies. The interconnection mechanism 506 enables communications, including instructions and data, to be exchanged between system components of the controller 500.

The controller 500 can also include one or more user interface devices 508 and system interface devices 512 such as input devices, output devices and combination input/output devices. Interface devices may receive input or provide output. More particularly, output devices may render information for external presentation. Input devices may accept information from external sources. Examples of user interface devices include keyboards, mouse devices, trackballs, microphones, touch screens, printing devices, display screens, speakers, network interface cards, etc. Interface devices allow the controller to exchange information and to communicate with external entities, such as users and other systems via digital or analog input or output streams.

The data storage element 510 includes a computer readable and writeable data storage medium configured to store non-transitory instructions and other data, and can include both nonvolatile storage media, such as optical or magnetic disk, ROM or flash memory, as well as volatile memory, such as RAM. The instructions may include executable programs or other code that can be executed by the at least one processor 502 to perform any of the functions described herein.

Although not illustrated in FIG. 5, the controller 500 may include additional components and/or interfaces, such as a communication network interface (wired and/or wireless), and the at least one processor 502 may include a power saving processor arrangement.

Referring now to FIG. 6, and with continuing reference to FIG. 0.1, illustrated is one example of a magnetic field detector 600 including a separated proof-mass (e.g., proof-mass 102 illustrated in FIG. 1) and magnetic dipole source. The detector 600 may be included in one or more of the examples of systems described herein, such as the magnetic field detector system 100 illustrated in FIG. 1. That is, the detector 600 may be coupled with the controller 112, displacement sensor 114, and field concentrators 116, among other components of the system 100 illustrated in FIG. 1.

As discussed with reference to FIG. 1, in certain examples, the magnetic dipole source may include a plurality of magnetic sources stacked or separated in a predetermined arrangement. The example of FIG. 6 illustrates a separated proof-mass including a first portion 602 and a second portion 604 divided by an isolation structure 606. Accordingly, in certain examples the magnetic dipole source may include a first portion that is formed on or attached to the first portion 602 of the proof-mass, and a second portion that is formed on or attached to the second portion 602 of the proof-mass. In certain other examples, the proof-mass may be formed from the magnetic dipole source. That is, the proof-mass (e.g., first and second portion 602, 604) may be composed of a permanent magnetic material or a time-varying magnetic material.

As further discussed below with reference to at least FIGS. 8 and 9A-9B, various embodiments may include one or more relief restructures, such as a geometric isolation structure and/or an internal isolation structure. Each of the isolation structures may be positioned to isolate the supports 608, 610 from a differential thermal strain between the proof-mass (e.g., first portion 602 and second portion 604) and the supports 608, 610. Such an arrangement may improve the noise performance and/or magnetic field sensitivity of the magnetic field detector 600.

In the example of FIG. 6, each support structure 608, 610 is coupled to the internal isolation structure 606, which is arranged as a bridge between the first portion 602 of the proof-mass and the second portion 604 of the proof-mass. Each portion 602, 604 may include a magnetic dipole source magnetized in a common direction with the other magnetic dipole source. In particular implementations, the each portion 602, 604 of the proof-mass may be mounted onto a substrate 612, 614. As will be appreciated by those skilled in the art, given the benefit of this disclosure, FIG. 6 shows one example of an arrangement of a separated proof-mass, and other variations in size, shape, and location of the proof-mass can be implemented and are within the scope of this disclosure.

For example, FIG. 7 illustrates another arrangement of an example of a magnetic field detector 700 in which the proof-mass is separated into four portions 702, 704, 706, 708. Similar to the detector 600 illustrated in FIG. 1, the detector 700 may be included within one or more of the magnetic field detector systems described herein. Much like, the portions 602, 604 of the proof-mass illustrated in FIG. 6, each of the portions 702, 704, 706, 708 shown in FIG. 7 may include a magnetic dipole source which is magnetized in a common direction relative to the other magnetic dipole sources. Each portion 702, 704, 706, 708 of the proof-mass may be coupled to a shared substrate 710 which is common to each of the portions 702, 704, 706, 708 of the proof-mass. As further illustrated, in such an arrangement a plurality of supports 712, 714 may be interposed between the portions 702, 704, 706, 708 of the proof-mass, and coupled to the shared substrate 710.

Referring to FIG. 8, illustrated is an example of a magnetic field detector system 800 including a plurality of geometric isolation structures 812, 814. As discussed above, in various embodiments the geometric isolation structures 812, 814 may isolate a plurality of supports 804, 806, 808, 810 from a differential thermal strain between a proof-mass 802 and the plurality of supports 804, 806, 808, 810. In particular, FIG. 8 demonstrates an example of an “H-shaped” arrangement which may reduce the sensitivity of the system 800 to errors by substantially isolating the plurality of supports 804, 806, 808, 810 from thermal deformations. In the example of FIG. 8, a first geometric isolation structure 812 is interposed between a first support 804 and the proof-mass 802, and a second support 806 and the proof-mass 802. Similarly, a second geometric isolation structure 814 is interposed between a third support 808 and the proof-mass 802, and a fourth support 810 and the proof-mass 802. Each support 812, 814 may suspend the proof-mass 802 relative to a mounting surface, such as a shared substrate 816 (e.g., silicon substrate). The shared substrate 816 may support additional components of the system 800, and may provide routing for electrical contacts 818. Electrical contacts 818 may be used to electrically couple various components of the system 800, such as a first, second, third, and fourth sensor and a controller.

In the illustrated example, the first geometric isolation structure 812 and the second geometric isolation structure 814 suspend the proof-mass 802 in an opening 820 defined by the shared substrate 816. The opening 820 in the substrate may allow access to a backside of the proof-mass 802, which may make attaching the magnetic dipole source easier. As illustrated, each geometric isolation structure 812, 814 includes a first arm (e.g., fork-shaped arm) coupled to the proof-mass 802 and a second arm (e.g., serpentine-shaped arm) coupled to the respective supports. As shown, each of the geometric isolation structures 812, 814 extend in a direction across the opening that is substantially parallel to a direction of extension of the respective supports. Accordingly, the geometric isolation structures 812, 814 position each support 804, 806, 808, 810 in an orientation that is substantially orthogonal to a direction of thermal expansion of the proof-mass 802. Accordingly, the system 800 includes one or more geometric isolation structures 812, 814 to geometrically reduce the thermal sensitivity of each of the supports 804, 806, 808, 810. In the shown example, each of the support beams 804, 806, 808, 810 is split into a fork to further reduce damping losses.

As also discussed herein, certain embodiments of a magnetic field detector system may also include one or more internal isolation structures positioned to isolate a plurality of supports (e.g., supports 104, 106, 132, 138 shown in FIG. 1) from a differential thermal strain between a proof-mass (e.g., proof-mass 102 shown in FIG. 1) and the respective supports. Referring to FIGS. 9A-9B, illustrated is an example of a magnetic field detector system 900 including an internal isolation structure 912. In particular, FIG. 9A shows a perspective view of the magnetic field detector system 900, and FIG. 9B shows a plan view of the magnetic field detector system 900. In the example of FIGS. 9A and 9B, the internal isolation structure 912 is interposed between a first support 904, a second support 906, a third support 908, a fourth support 910, and a proof-mass 902. Moreover, FIGS. 9A and 9B demonstrate an example of an “X-shaped” arrangement in which each of the supports 804, 806, 808, 810 has a reduced size to maximize a scale factor and improve the performance of the system 900.

As illustrated in FIG. 9B, the internal isolation structure 912 extends through the proof-mass 902 and suspends the proof-mass 902 within an opening 914 defined in a mounting surface, such as a shared substrate 916 (e.g., silicon substrate). In particular, the internal isolation structure 912 may define an aperture along an exterior (e.g., perimeter) of the proof-mass 902 (e.g., illustrated as groove 918). The aperture provides an air gap between the proof-mass 902 and the supports 904, 906, 908, 910, and allows the proof-mass 902 to expand and/or contract without an effect on the respective supports 904, 906, 908, 910. Accordingly, the system 900 includes one or more internal isolation structure 912 which reduce the thermal sensitivity of each of the supports 904, 906, 908, 910. As discussed with reference to the system 800 illustrated in FIG. 8, each of the support beams 804, 806, 808, 810 may be split into a fork to further reduce damping losses. Further, the shared substrate 916 may support additional components of the system 900, and may provide routing for electrical contacts 920. Electrical contacts 920 may be used to electrically couple various components of the system 900 (e.g., the first, second, third, and fourth sensors and the controller 112 shown in FIG. 1).

Referring now to FIG. 10, illustrated is one example of a magnetic field detector system 1000 packaged within a housing. In certain examples, the housing may facilitate a vacuum environment or cryogenic environment to further reduce damping effects within the system 1000. In the shown example, the housing includes a top cover 1002, an intermediate mounting surface 1004, and a bottom cover 1006. However, in certain other examples the housing may be arranged in other appropriate configurations. In particular implementations, the housing includes one or more attachments which secure the housing to a mobile platform, such as a vehicle. In certain other implementations, the housing may include one or more attachments which secure the housing to a stationary platform.

In various embodiments, the system 1000 may include many of the same components as the system 100 illustrated in FIG. 1 (e.g., the proof-mass 102, the sensors, the plurality of supports, the controller 112, etc.), which are not explicitly described with reference to FIG. 10 for the convenience of description. As illustrated, components of the system 1000 may be mounted on a shared substrate, such as the illustrated printed circuit board 1008. The printed circuit board 1008 may be attached to the bottom cover 1006 of the housing. An internal shield 1010 may extend from the bottom cover 1006 to shield portions of the printed circuit board 1008 and reduce noise interference from electronic components of the system 1000. In certain examples, the internal shield 1010 may be composed of a non-conductive material with a high magnetic permeability.

As illustrated, in certain embodiments the system 1000 may include one or more field concentrators 1012 positioned and arranged to focus the magnetic field on the proof-mass. For example, the field concentrators 1012 may include various flux concentrators, such as soft magnetic materials. The field concentrators 1012 may be positioned on the intermediate mounting surface 1004 which is configured to rest on a top surface of the internal shielding 1010. When coupled with the internal shielding 1010, an opening 1014 defined in the intermediate mounting surface 1004 rests substantially proximate the proof-mass so as to permit the receipt of magnetic radiation at a proof-mass of the system 1000. As further illustrated in FIG. 10, in certain examples the system 1000 may be enclosed by a top cover 1002.

Having described above several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the disclosure. Accordingly, the foregoing description and drawings are by way of example only, and the scope of the disclosure should be determined from proper construction of the appended claims, and their equivalents. 

What is claimed is:
 1. A magnetic field detector system comprising: a proof-mass including a magnetic dipole source; a plurality of supports, each individual support of the plurality supports being coupled to the proof-mass; a plurality of sensors, each individual sensor of the plurality of sensors positioned to measure a resonant frequency of a corresponding support of the plurality of supports; and a controller coupled to each individual sensor of the plurality of sensors, the controller configured to measure a characteristic of a magnetic field imparted on the proof-mass based on at least a first resonant frequency of the measured resonant frequencies.
 2. The magnetic field detector system of claim 1, wherein the controller is further configured to determine a linear force imparted on the proof-mass, in a first direction, based on at least the first resonant frequency of the measured resonant frequencies.
 3. The magnetic field detector system of claim 1, wherein the controller is further configured to determine a temperature based on a common mode signal generated from a comparison of each of the measured resonant frequencies.
 4. The magnetic field detector system of claim 1, wherein the characteristic of a magnetic field includes a magnetic field strength, and wherein in measuring the characteristic of the magnetic field the controller is configured to compare at least the first resonant frequency to a first frequency reference to measure a torque on the proof-mass.
 5. The magnetic field detector system of claim 4, wherein the measured resonant frequency of each individual support includes a natural frequency.
 6. The magnetic field detector system of claim 1, wherein the plurality of supports includes a first support coupled to a first side of the proof-mass and having the first resonant frequency, a second support coupled to a second side of the proof-mass and having a second resonant frequency, a third support coupled to the first side of the proof-mass and having a third resonant frequency, and a fourth support coupled to the second side of the proof-mass and having a fourth resonant frequency.
 7. The magnetic field detector system of claim 6, wherein the controller is further configured to determine a first linear force imparted on the proof-mass in a first direction and a second linear force imparted on the proof-mass in a second direction based on the first resonant frequency, the second resonant frequency, the third resonant frequency, and the fourth resonant frequency, and determine a temperature based on a common mode signal generated from a comparison of each of the first resonant frequency, the second resonant frequency, the third resonant frequency, and the fourth resonant frequency.
 8. The magnetic field detector system of claim 1, wherein the magnetic dipole source is a permanent magnetic material.
 9. The magnetic field detector system of claim 8, wherein the permanent magnetic material is at least one of a Neodymium Iron Boron (NdFeB) magnet, a Samarium Cobalt (SmCo) magnet, and an Alnico (AlNiCo) magnet.
 10. The magnetic field detector system of claim 1, wherein the magnetic dipole source includes a plurality of permanent magnetic materials magnetized in a common direction.
 11. The magnetic field detector system of claim 1, wherein the magnetic dipole source is a time-varying magnetic material.
 12. The magnetic field detector system of claim 11, wherein the time-varying magnetic material is a soft magnetic material configured to receive an excitation signal of a predetermined frequency.
 13. The magnetic field detector system of claim 12, wherein the soft magnetic material is Magnesium Zinc Ferrite.
 14. The magnetic field detector system of claim 1, wherein each sensor of the plurality of sensors includes a comb drive including a first electrode configured to apply a voltage to a comb positioned on the corresponding support, and a second electrode configured to measure a change in a capacitance between the first electrode and the second electrode, wherein the controller is further configured to infer the resonant frequency of the corresponding support based at least in part on the change in the capacitance.
 15. The magnetic field detector system of claim 1, further comprising a field concentrator located adjacent a side of the proof-mass, the field concentrator positioned so as to focus the magnetic field on the proof-mass.
 16. The magnetic field detector system of claim 1, further comprising a plurality geometric isolation structures interposed between the proof-mass and each of the plurality of supports, each geometric isolation structure being positioned to isolate a respective support from a differential thermal strain between the proof-mass and the respective support.
 17. The magnetic field detector system of claim 1, further comprising an internal isolation structure extending through the proof-mass and configured to suspend the proof-mass relative to a system substrate, the internal isolation structure being positioned to isolate the plurality of supports from a differential thermal strain between the proof-mass and the plurality of supports.
 18. A magnetic field transduction method comprising: generating a magnetic dipole at a proof-mass coupled to a plurality of supports; receiving a magnetic field at the proof-mass; measuring a resonant frequency of each individual support of the plurality of supports; and determining a characteristic of the magnetic field based on at least one resonant frequency of the measured resonant frequencies of the individual supports.
 19. The method according to claim 18, wherein determining the characteristic of the magnetic field further comprises comparing the at least one resonant frequency to a frequency reference and determining a torque imparted on the proof-mass.
 20. The method according to claim 19, wherein determining the characteristic of the magnetic field includes determining the strength and variability of the magnetic field.
 21. The method according to claim 18, further comprising determining a linear force imparted on the proof-mass in a first direction based on the at least one resonant frequency of the measured resonant frequencies of the individual supports.
 22. The method according to claim 18, further comprising determining a temperature based on a common mode signal generated from a comparison of each of the measured resonant frequencies of the plurality of supports.
 23. The method according to claim 18, further comprising determining a force of acceleration imparted on the proof-mass based on the at least one resonant frequency of the measured resonant frequencies of the individual supports.
 24. The method according to claim 18, wherein the measured resonant frequency of each individual support of the plurality of supports includes a natural frequency.
 25. The method according to claim 18, further comprising optically sensing a displacement of the proof-mass responsive to receiving the magnetic field.
 26. The method according to claim 18, further comprising sensing a variation in a capacitance between the proof-mass and a reference structure responsive to receiving the magnetic field.
 27. The method according to claim 18, wherein the plurality of supports includes a first support having a first resonant frequency, a second support having a second resonant frequency, a third support having a third resonant frequency, and a fourth support having a fourth resonant frequency, and wherein the method further comprises: determining a first linear force imparted on the proof-mass, in a first direction, based on the first resonant frequency, the second resonant frequency, the third resonant frequency, and the fourth resonant frequency; determining a second linear force imparted on the proof-mass, in a second direction, based on the first resonant frequency, the second resonant frequency, the third resonant frequency, and the fourth resonant frequency; and determining a temperature based on a common mode signal generated from a comparison of each of the first resonant frequency, the second resonant frequency, the third resonant frequency, and the fourth resonant frequency.
 28. A magnetic field transduction method comprising: generating a magnetic dipole at a proof-mass coupled to a plurality of supports; receiving a magnetic field at the proof-mass; optically sensing a displacement of the proof-mass responsive to receiving the magnetic field; and determining a characteristic of the magnetic field based on at least the displacement of the proof-mass.
 29. A magnetic field transduction method comprising: generating a magnetic dipole at a proof-mass coupled to a plurality of supports; receiving a magnetic field at the proof-mass; sensing a variation in a capacitance between the proof-mass and a reference structure responsive to receiving the magnetic field; and determining a characteristic of the magnetic field based on at least the variation in the capacitance between the proof-mass and the reference structure. 